PRELIMINARY PERFORMANCE
ANALYSIS of 'mid 2011' iMac

Posted Tuesday, May 3rd, 2011, by rob-ART morgan, mad scientist
Updated May 4th with Q&A section and new info.
Updated May 5th with good news on 6Gb/s port issue.

Here are the KEY PERFORMANCE FEATURES of the 2011 iMac which appeared on the Apple online store today:

CPU chipset upgraded
The Sandy Bridge chipset used in the 2011 MacBook Pro is now in the iMac. The top model quad-core Core i7 is now available at 3.4GHz. It can run as fast as 3.8GHz when Turbo Boost kicks in and create up to 8 virtual cores when Hyper-Threading is required. Though all 2011 models of iMac have quad-cores, only the Core i7 models have Hyper-Threading.

THUNDERBOLT port added
As with the 2011 MacBook Pros, it now has two fast Thunderbolt ports with 10-Gb/s data channels. That's 12 times faster than the FireWire 800 port -- previously the fastest built-in iMac external data port.

GPU upgrade
The top model now sports a Radeon HD 6970M with 1GB of GDDR5 video memory. Apple claims it is up to 3 times faster than the previous generation of iMac GPU. There is a CTO option for 2GB of video memory. Do you need 2GB? When I ran Portal 2's intro sequence, I saw as much as 96% video memory usage (according to atMonitor) on the 2010 Mac Pro with 1G of VRAM. Also, if you plan one or two external displays, extra video memory comes in handy.

The rest of the iMac models have either a Radeon HD 6750M or 6770M with 512MB of video memory.

Dual internal drives
This is not a new feature but is a welcome continuation. You can custom order it with an internal SSD and internal HDD. FLASH: The 2011 iMac EFI update enables 6Gb/s mode on two internal SATA ports.

PRELIMINARY ANALYSISIt's great to see the performance enhancements in the GPU and CPU but the Thunderbolt port is the icing on the cake. It will be interesting to know stats on how many owners of older Mac Pros upgrade to a 2011 iMac instead of a newer Mac Pro.

21" Core i5

21" Core i5

21" Core i7

27" Core i5

27" Core i5

27" Core i7

CPU

SR005

SR009

SR00E

SR009

SR00Q

SR00B

TDP*

65W

65W

65W

65W

95W

95W

Frequency

2.5GHz

2.7GHz

2.8GHz

2.7GHz

3.1GHz

3.4GHz

TurboBoost

3.3GHz

3.7GHz

3.8GHz

3.7GHz

3.4GHz

3.8GHz

Phys. Cores

4

4

4

4

4

4

Hyper Threads

4

4

8

4

4

8

GPU

R6750M

R6770M

R6770M

R6770M

R6970M

R6970M

VRAM

512MB

512MB

512MB

512MB

1GB**

1GB**

(*TDP = Thermal Design Power; ** 2GB optional)

QUESTIONS? ANSWERS!"Should I order the iMac with 2GB of video memory or is 1GB enough?"
It depends on what apps you are running. Some apps use a large percentage of video memory (VRAM) and some don't. I suggest you analyze your work flow (or game play) using atMonitor or similar utility to see what percentage of VRAM is in use. For example, when I ran Portal 2's intro sequence, I saw as much as 86% video memory usage on the 2010 iMac with the Radeon HD 5750 with 1G of VRAM. So for Portal 2 users, the 2GB option is a good idea. Also keep in mind that the use of VRAM will only increase as software technology advances. So having more VRAM than you need now is known as "future proofing."

"Will the 2011 iMac support two external 27" LED Cinemas since it has two Thunderbolt ports?"
Yes. We have two external 27" LED Cinemas connected to our 2011 iMac with 27" display. All three are running at 2560x1440. (And with the 2GB video memory option, we have plenty to go around.)

"Does the 2011 iMac have 6Gb/s internal SATA ports?"
Initial information from our sources was that the 6Gb/s mode was enabled on SATA ports 0 and 1, but testing by the OWC lab with a 6Gb/s SSD on all three 27" models showed only 3Gb/s speeds on all three ports. FLASH: The 2011 iMac EFI update posted May 5th enables 6Gb/s mode on internal SATA ports 0 and 1. The optical port runs at 3Gb/s.

"Is there any downside to replacing the factory drives?"
Installing any non-factory HDD in the 2011 iMac causes the fans to run at full speed. If you keep the factory HDD but add a third party SSD, the fans run as normal.

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